Anti-fouling covering for use in sub-sea structures

ABSTRACT

An anti-fouling covering is applied to a tubular offshore structure to prevent fouling tubular goods by marine growth. The covering comprises metal sheeting which is deformed to provide spaced ridges or troughs which extend on the covering in the axial direction of the tubular goods. The deformations facilitate expansion and contraction of the covering but, especially when inwardly directed trough form, enable the covering to have substantially smooth exterior so that loading due to wave impingement can be reduced.

This invention relates to a covering to protect tubular members ofsub-sea structures particularly offshore structures from fouling bymarine organisms or growths and also to a process for applying thecovering. The present invention also relates to a tubular compositeincluding an anti-fouling covering.

The fouling of marine structures by marine growths involving marineorganisms is well known. Since these growths can adversely affect thewellbeing of the structure, it is necessary from time-to-time to carryout cleaning operations to remove the growths but there is thedisadvantage that these cleaning operations are invariably costly. Thisproblem can be particularly severe with tubular structures as these aregenerally immersed at considerable depths where marine growths such asmussel formation is especially prevalent.

To avoid or minimise the above problem it is known to cover or cladappropriate parts of the structure with copper or copper nickel plating,with insulating material located between the sheeting and the structure.Particular examples of such covering comprise (a) half-shells (forfitting around tubular members) and (b) copper-nickel wire mesh embeddedin an elastomer or epoxy matrix. However a particularly advantageous forof anti-fouling sheet covering is described in the present applicants'International application PCT/GB88/00403 (published as W088/09460) whichsheet covering comprises anti-fouling metal which is corrugated. In thepreferred form of application of the corrugated sheeting to a tubularmember, a corrugated metal strip of anti fouling material is wound ontoan insulating layer, for example of elastomers or epoxies, on thetubular member such that the metal strip covers the tubular member.

It is an object of the present invention to provide an improvedanti-fouling covering relative to the-covering of Internationalapplication W088/09460.

According to one aspect of the present invention there is provided acovering to protect a tubular sub-sea structure from fouling by marineorganisms, said covering comprising metal sheeting (13) wrapping thesub-sea structure (11) and serving to prevent or mitigate the build-upof fouling growths on the sub-sea structure (11), said metal sheeting(13) comprising corrugated sheeting whereby valley-form sheetingdeformation (14) extend in the axial direction on the sub-sea structurecharacterized in that only a limited number of circumferentially spacedvalley-form deformations (14) are present on the metal sheeting (13),the sheeting portion (13A) between the spaced deformations (14)comprising substantially plain metal.

The present invention is also a covering to protect sub-sea structuresfrom fouling by marine growths comprising metal sheeting (13) wrappingthe sub-sea structure (11) and serving to prevent or mitigate thebuild-up of fouling growths on the sub-sea structure (11), said metalsheeting (13) comprising corrugated sheeting whereby valley-formsheeting deformation (14) extend in the axial direction on the sub-seastructure characterized in that the metal sheeting (13) has at least onevalley-form deformation (14, FIG. 3) which extends inwardly relative tothe sub-sea structure (11), the sheeting portions (13A) on either sideof said one valley-form deformation (14) being substantially plain.

Preferably the metal sheeting is in strip form with the deformationextending transversely on the strip, and preferably the deformationextends to opposed edges of the strip, i.e. each ridge or trough isdefined by a corrugation. The metal sheeting is preferably of copper orcopper nickel material.

Preferably the ridges or troughs are spaced by non-deformed areas on thesheeting such that the total area of the deformations is not greaterthan 70% of the total area of the sheeting, and preferably no greaterthan 40% of the total area: in a preferred embodiment the deformationarea is less than 20% of the total sheeting area.

The present invention is also a tubular composite for use in a sub-seastructure; said tubular composite comprising a base tube, and an outeranti-fouling covering; said anti-fouling covering comprisinganti-fouling metal sheeting which is deformed to provide spaced ridgesor troughs.

Preferably no more than ten longitudinally-extending deformations areprovided around the circumference of the tubular composite with respectto one cross-section of the composite.

According to another aspect of the present invention there is provided aprocess for applying an anti-fouling covering to a tubular member of asub-sea structure to protect said member from fouling by marine growths,comprising the steps of applying a coating of elastomeric anti-corrosionmaterial to the outer surface of the tubular member, applyinganti-fouling sheet covering having valley form deformations to theelastomeric coating to enclose the tubular member whereby thevalley-form deformations extend axially, applying a moulding pressure onthe sheet covering to provide a restricting force thereto and to apply abond between the sheet covering and the elastomeric material, andvulcanizing the elastomeric material, the arrangement being such thatthe deformations of the anti-fouling covering allow movement of anychanges on the circumference of the elastomeric coating to beaccommodated during and after the vulcanization process without unduestress on the bond between the coating and the sheet coveringcharacterized in that for the anti-fouling sheet covering there is usedmetal sheeting provided with only a limited number of valley-formdeformations, the sheeting portions between valley-form deformationscomprising substantially plain metal.

The anti-fouling sheet covering is preferably applied by winding stripmaterial around the tubular member. The strip can have any suitablewidth, say for example 150 mm, and thickness say 0.5 mm to 2 mm. Thedeformation can be applied to the sheet material by means of suitablemetal deforming apparatus or by a metal stamping machine, and the size(height) of the deformations can be selected as desired, the deformationheight generally being dependent on the diameter of the tubular memberto be covered.

Before it is applied to the elastomer coating, the strip will bechemically or mechanically cleaned and a bonding agent is preferablyapplied on the strip surface contacting the elastomer coating.

According to a further aspect of the present invention, there isprovided an anti-fouling covering assemblage for fitting to a tubularstructure comprising a plurality of part circular, preferablysemi-circular, covering units (41A), 41B) each unit including a metalsheeting part (13), characterized in that the sheeting parts (13)provide at least one valley-form indentation or corrugation, when theassemblage is fitted on a tubular structure (11)k, sheeting portions oneither side of the valley-form indentation (14) being of substantiallyplain form.

Preferably the sheeting parts are bonded to a coating layer for locationbetween the sheeting and the tubular structure, and the assemblage canbe secured to a tubular structure, e.g. pipe by any suitable means, forexample by straps or bands.

By means of the present invention, the metal sheet covering canrepresent a substantially clean cylinder without major exteriorobstructions and this will encourage lower loading to be encounteredduring fluid loading when in use in a sub-sea environment. However, theindentation will facilitate expansion and contraction in the covering.

Embodiments of the present invention will now be described by way ofexample with reference to the accompanying drawings wherein:

FIG. 1 shows a schematic pictorial view of a covering of the presentinvention applied to a pipe;

FIG. 2 shows the deformed, trough, part of portion A of FIG. 1 to alarger scale;

FIG. 3 shows an end view of the covering as fitted to a pipe or conduit;

FIG. 4 shows a schematic view of the covering being applied to a pipe;

FIG. 5 shows a retro-fit covering assemblage in accordance with thepresent invention; and

FIGS. 6 and 7 shows further forms of covering unit.

Referring to the drawings, FIG. 4 illustrates the formation of aprotected tubular marine structure, i.e. sub-sea structure 10 in thisembodiment, more especially a covered pipe 11 for the supply or deliveryof fluid, and it is shown with portions cut away for clarity. Othertubular structures, such as legs or jackets of off-shore structures, maybe similarly protected.

The structure 10 comprises a length of steel pipe 11 the outer surfaceof which is completely coated with an anti-corrosion material 12 andthen totally encapsulated with a strip of anti-fouling metallic material13 such as copper or copper nickel. The strip is applied in a spiralmanner by hand or by machine while rotating the coated pipe. Prior toapplication to the coated pipe 11, the metallic strip 13 is deformed toprovide a series of transverse indentations 14, each in the form of acorrugation, the indentations 14 extending from one side of non-deformedsurface portions 13A as is best seen in FIG. 3, the size of each surfaceportion 13A defining the spacing of the indentations. The indentations(corrugations) 14 can be applied by means of suitable metal deformingapparatus, such as roller apparatus or a metal stamping machine.

Also, the metallic ridged strip 13 is chemically or mechanically cleanedand a bonding agent is applied to the surface of the strip contactingthe material 12 before the strip is wound onto the coated pipe 11.

When the strip 13 is wound spirally onto the pipe 11, the indentations14 extend longitudinally or essentially longitudinally of the pipe toform inwardly directed troughs (as can be seen in FIG. 3). Theconvulations of the spirally would strip 13 may be arranged simply tohave edge abutment but a slight overlap of the convulations would alsobe possible to ensure satisfactory covering of the pipe.

The anti-corrosion coating 12 may be an epoxy resin which after themetal strip has been wound into the pipe, is cured chemically in amanner known per se in the art. Preferably however, the anti-corrosioncoating is an elastomeric material.

Once the strip 13 has been wound onto the pipe 11 coated with anelastomeric material, a temporary covering, not shown is wrapped-aroundthe metallic covering, e.g. a nylon tape applied at high pressure, e.g.70-120 Kilos to provide a restricting force, over the full length of themetallic covering, and thereafter the elastomeric material is vulcanisedat, for example 110°0 to 170° C. to form an elastomer. On completion ofthe vulcanisation process the temporary covering can be removed.

The space between the strip covering 13 and the pipe 11 is fully filledwith elastomeric material 12, the winding of the strip 13 onto thecoated pipe 11, (using the application process above described)resulting in the troughs 14 pressing into the coating 12. On coolingafter vulcanisation, the differential in contraction of the elastomerand metal covering is accommodated due to the strip covering having theability to have annular displacement (by virtue of the troughs 14) oreven deform. On contraction of the elastomer the deformation of themetal covering is therefore evenly distributed.

The elastomer bond so formed can now accommodate the differing rates ofcontraction and expansion of the elastomer 12 and anti-fouling strip 13by virtue of the troughs 14. Furthermore the elastomer vulcanised withinthe troughs 14 as shown in FIG. 7 will enable the anti-fouling strip 13to better withstand impacts.

It is a feature of the arrangement that only a limited number of troughs14 are arranged on the circumference of the covered pipe 11 (consideredwith regard to a single cross-section of the covered pipe as shown onFIG. 3--in practice a series of staggered deformations 14 will bepresent along the length of the pipe as shown in FIG. 1. In particular 4such troughs 14 are present in FIG. 3 and it is preferable that thereshould be no more than about 10: consequently the total area of theindent ridges 14 will in general be less than 20% of the total area ofthe strip 13 and in any event will be no more than 70% of the striptotal area.

The profile of the indentation 14 will be suitably chosen, particularlywith regard to the width (W) to depth (D) ratio of the indentation andthis will be especially dependant on the diameter of the pipe, but byway of example W/D could be greater than two. Only a limited number ofindentations 14 are present circumferentially at one section, butpreferably two or more are present. In any event it is preferred thatthe projected circumferential area of the indentations 14 in combination(conveniently calculable using dimension W) is not greater than 20% ofthe total circumferential area of the covering. The coating 12, forexample 6 mm thick can be formed from polychloroprene (elastomer), whilethe metal sheeting 13 can comprise a 90/10 cupro-nickel cladding. Abreak 20 in the electrical continuity of the anti-fouling covering canbe present; and introduced after the covering has been applied.

The above covering arrangement conveniently allows expansion andcontraction of the pipe 11 and elastomer coating 12 to occur duringmanufacture or in service, while preventing or limiting stress betweenthe layers of the metal sheeting 13 and the coating 12. Further, theouter surface of the covering is essentially of a clean form withoutsubstantial obstruction, and indeed can approximate closely to a smoothcylinder, with the result that the co-efficient of drag (Cd) is kept toa low level so keeping fluid loading on the pipe assembly low when inuse in a sub-sea environment. The smooth covering form also avoidsobstructions when the assembly is passing through guides and clampsduring handling at the fabrication site.

In the case of a fully corrugated covering, waves will be able to get amore pronounced "grip" on the covering so increasing the wave loading onthe covered pipe (or tubular member), but such wave loading will beconsiderably reduced when a covering strip of the present invention isutilised.

The use of fewer corrugations will enable the use of less amount ofmaterial (for the same sheet thickness) to cover a given tubular area.

While the above related to a complete covered pipe assembly 10, it wouldbe possible to have the covering as a separate asemblage to serve as aretro-fit system on an existing pipe installation In an example offorming such an assemblage, the previously described covered pipeforming procedure could be utilised generally but in this case nobonding agent would be present between the pipe 11 and the coating 12 sopreventing a bond between the pipe and the elastomer coating--the pipe11 effectively serving as a form of mandrel. The metal sheeting 13 wouldbe applied as previously. After the covering has been formed and thecoating cured, this covering will be cut longitudinally as indicated atL in FIG. 3 (and by dashed line L in FIG. 1) and possibly alsocircumferentially at convenient lengths (for example at 2 meters). Theassemblage 21A, (shown in FIG. 5) can then be removed from thepipe/mandrel 11 by virtue of the flexibility of the assemblage, andplaced in readiness for fitting to existing tubulars of similar size,for example off-shore. The assemblage 21A, can be secured on the tubularby any suitable means, for example by straps or bands 22. In analternative arrangement shown in FIG. 6 integral one-piece semi-circularmetal sheets are used to form integral parts 41A, 41B, formed forexample by stamping on a die/mandrel, and the coating 12 can be appliedat an appropriate time.

The spacing of the deformations 14 and the (helix) angle of thedeformations 14 relative to the tubular member axis will be determinedby the diameter of the tubular member and by the likely environmentalconditions in which the member operates. Sub-sea structures includingcovered tubular members in accordance with the present invention can beused in both shallow and deep water environments.

Instead of having the deformations 14 as inwardly directed troughs, itay be preferred in some circumstances to have the deformations 14 of thecovering as outwardly directed ridges as shown in FIG. 7 but a limitednumber of these ridges would be present just as in the case of troughs.In the formation of the covering with ridges, the elastomer 12 will flowinto the convex spaces of the ridges during vulcanisation. In a furthermodification, the anti-fouling strip could have a combination of ridgesand troughs (circumferentially spaced by on-deformed metal sheetportions.

I claim:
 1. A covering to protect a tubular subsea structure fromfouling by marine organisms, said covering comprising:means wrapping thesubsea structure including metal sheeting and serving to prevent ormitigate the buildup of fouling growths on the subsea structure, saidmeans comprising a helically wound strip means defining a series ofspaced valley-form deformation means extending transversely on the stripmeans, portions of said strip means between the deformation means beingsubstantially planar, said deformation means being arranged such that,when the means wrapping the subsea structure is located on the tubularstructure to be protected, at least one deformation means is presentcircumferentially in each 360` turn of said strip means.
 2. A coveringto protect a tubular subsea structure from fouling by marine organisms,said covering comprising:means wrapping the subsea structure includingmetal sheeting and serving to prevent or mitigate the buildup of foulinggrowths on the subsea structure, said means comprising a helically woundstrip means defining a series of spaced valley-form deformation meansextending tranveresely on the strip means, said strip means applied tothe tubular structure so that the covering defines valley-formdeformation means which are radially inwardly directed, portions betweenthe deformation means being substantially planar, said deformation meansbeing arranged such that when the means wrapping the subsea structure islocated on the tubular structure to be protected, at least one radiallyinwardly directed deformation means is present circumferentially in each360° turn of said strip means.
 3. A covering as claimed in claim 1 or 2,wherein said deformation means extends to opposed edges of said stripmeans.
 4. A covering as claimed in claim 1 or 2, wherein the metalsheeting is of copper or copper/nickel material.
 5. A covering asclaimed in claim 1 or 2, wherein at any one transverse section of thecovering, there are no more than ten of said deformation means presentfor each 360° turn of said strip means.
 6. A covering as claimed inclaim 1 or 2, wherein the covering comprises a flexible, open-sided,annular assemblage which is deformable to fit into a tubular member. 7.An anti-fouling covering assemblage for fitting to a tubular structure,comprising:a plurality of substantially semi-cylindrical covering means,each covering means including a metal sheeting part, said sheeting partsproviding at least one valley-form deformation means, such that when theassemblage is fitted on a tubular structure, portions between thedeformation means are substantially planar.
 8. The assemblage as inclaim 7, wherein the valley-form deformation means is inwardly directed.9. The assemblage as in claim 7 or 8, wherein the sheeting parts arebonded to a coating layer, said coating layer being located between thesheeting and the tubular structure.
 10. A tubular composite for use in asubsea structure, said tubular composite comprising a base tube and anouter anti-fouling covering means wrapping the base tube, saidanti-fouling covering means comprising anti-fouling metal sheeting whichis deformed to provide ridges and troughs, said metal sheeting beingformed by helically wound strip means, said strip means defining aseries of spaced valley-form deformation means extending transversely onthe strip means, portions of said strip means between the deformationmeans being substantially planar, said deformation means arranged suchthat, when the sheeting is located on the tubular structure to beprotected, at least one deformation means is present circumferentiallyin each 360° turn of said strip means.
 11. A process for applying ananti-fouling covering to a tubular member of a subsea structure toprotect said member from fouling by marine growths, said processcomprising the steps of applying a coating of elastomeric anti-corrosionmaterial to the outer surface of the tubular member, applyinganti-fouling sheet covering having valley-form deformations to theelastomeric coating to enclose the tubular member whereby thevalley-form deformations extend axially, and are present in eachtransverse section of the tubular member applying a molding pressure onthe sheet covering to provide a restricting force thereto and to apply abond between the sheet covering and the elastomeric material, andvulcanizing the elastomeric material, the arrangement being such thatthe deformation of the anti-fouling covering allow movement of anychanges on the circumference of the elastomeric coating to beaccommodated during and after the vulcanization process within unduestress on the bond between the coating and the sheet covering, whereinthe anti-fouling sheet covering comprises strips wound helically on theelastomeric coating, said strip having spaced deformations which extendtransversely on the strip and provide said valley-form deformations ofthe covering, the strip portions between the spaced deformations beingsubstantially plain.